1. Field of the Invention
The present invention relates to a tunneling magnetic sensing element, which is mounted on a hard disk or is used as an MRAM (Magnetic Random Access Memory), for example. More specifically, the present invention relates to a tunneling magnetic sensing element including an Mg—O insulating barrier. The element can increase a high resistance change ratio (ΔR/R) while maintaining favorable soft-magnetic properties of a free magnetic layer. The present invention further relates to a method of manufacturing the tunneling magnetic sensing element.
2. Description of the Related Art
In tunneling magnetic sensing elements, a resistance change is generated by a tunnel effect. When the magnetization of a pinned magnetic layer and the magnetization of a free magnetic layer are in anti-parallel alignment, a tunnel current flowing in an insulating barrier (tunnel barrier) disposed between the pinned magnetic layer and the free magnetic layer is reduced, and the resistance value becomes the maximum. On the other hand, when the magnetization of the pinned magnetic layer and the magnetization of the free magnetic layer are in parallel alignment, the tunnel current flows most easily and the resistance value becomes the minimum.
By using this phenomenon, an electric resistance change caused by a variation in magnetization of the free magnetic layer which is caused by influence of external magnetic fields is detected as a voltage change, and a leakage magnetic field from a recording medium is detected.
The properties, such as a resistance change ratio (ΔR/R), of a magnetic sensing element are varied by changing the material of an insulating barrier. Therefore, studies have been conducted for various materials used as insulating barriers.
The important properties of a tunneling magnetic sensing element are soft-magnetic properties such as resistance change ratio (ΔR/R), RA (element resistance R×area A), and magnetostriction λ and coercive force Hc of a free magnetic layer. These properties have been improved by optimizing materials and configuration of the insulating barrier, the pinned magnetic layer disposed on the top face of the insulating barrier, and the free magnetic layer disposed on the bottom face of the insulating barrier.
For example, in Patent Document 1, an insulating material used for an insulating barrier is disclosed in Japanese Unexamined Patent Application Publication No. 2004-179187 (refer to column [0036]). Related art configurations are disclosed in Japanese Unexamined Patent Application Publication No. 2004-179187, Japanese Unexamined Patent Application Publication No. 2005-50907, Japanese Unexamined Patent Application Publication No. 2005-116888, and Japanese Unexamined Patent Application Publication No. 2004-179183.
In the disclosure of above-mentioned Patent Documents, magnesium oxide (Mg—O) is used as the insulating barrier. In a tunneling magnetic sensing element having a lamination composed of, from the bottom, an antiferromagnetic layer, a pinned magnetic layer, an insulating barrier, and a free magnetic layer, a large resistance change ratio (ΔR/R) can be obtained by forming the insulating barrier by Mg—O and the free magnetic layer by CoFeB.
However, the magnetostriction λ of the free magnetic layer becomes large such as several tens ppm (for example, about 40 ppm as described below), which causes disadvantages the soft-magnetic properties of the free magnetic layer of deteriorate thereby, reducing the stability of reproducing characteristics.
The above-mentioned Patent Documents disclose not only materials for the insulating barrier but also materials for the pinned magnetic layer and the free magnetic layer (for example, Claim 1 of Japanese Unexamined Patent Application Publication No. 2004-179187 and column [0166] of Japanese Unexamined Patent Application Publication No. 2005-116888.
However, optimum materials and layer configuration of the pinned magnetic layer and the free magnetic layer when the insulating barrier is composed of Mg—O are not disclosed. No improvement in the structure (materials, composition ratio, and so on) of the free magnetic layer and the pinned magnetic layer has been conducted, in particular, in view of obtaining a high resistance change ratio (ΔR/R) while maintaining favorable soft-magnetic properties of the free magnetic layer when the insulating barrier is composed of Mg—O.